1. Field of the Invention
This invention relates to a rubber composition which is suitable for use in various rubber products including tires and industrial goods. More specifically, this invention relates to a rubber composition which is suitable for use in a tire tread having excellent flexibility at lower temperature and excellent gripping power.
This invention also relates to a tire in which the above-mentioned rubber composition is used.
2. Description of Related Art
In recent years, automobiles have been required to have low mileage and high safety. Accordingly, there is a demand for the improvement on gripping properties of a rubber composition which is used for the tread portion of a tire, both under wet conditions and dry conditions.
It is known that a butadiene rubber and a styrene-butadiene copolymer rubber of low bound styrene and low vinyl linkage proportions, which have conventionally been used widely for the tread portion of a tire, are excellent in low-temperature flexibility because of their low glass transition points (Tg) compared with other synthetic rubbers. They are therefore employed widely for the tread of a studless tire or an all-season tire.
A tread for which the butadiene rubber or the styrene-butadiene copolymer rubber having low bound styrene and low vinyl linkage proportions has been used is however accompanied with a problem that sufficient gripping properties cannot be obtained easily because of the low tan .delta. of the resulting rubber composition.
It is a common practice to lower the glass transition point (Tg) of a polymer so as to attain the low-temperature flexibility of a rubber composition. On the other hand, for an improvement of a gripping performance, it is necessary to raise Tg, thereby increasing tan .delta.. It is therefore difficult to satisfy these two performances at the same time.
Furthermore, a butadiene rubber or a styrene-butadiene copolymer rubber having low bound styrene and low vinyl linkage proportions are also accompanied with drawbacks that increase in its blending amount results in drop in processability such as roll winding property, and increase in shrinkage, thereby deteriorating the dimensional accuracy of the finished product.